Index: jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/ConcurrentCreateUserTest.java
===================================================================
--- jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/ConcurrentCreateUserTest.java	(revision 0)
+++ jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/ConcurrentCreateUserTest.java	(revision 0)
@@ -0,0 +1,84 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.jackrabbit.api.security.user;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.UUID;
+
+import javax.jcr.Node;
+import javax.jcr.RepositoryException;
+import javax.jcr.Session;
+
+import org.apache.jackrabbit.api.JackrabbitSession;
+import org.apache.jackrabbit.core.AbstractConcurrencyTest;
+import org.apache.jackrabbit.core.security.TestPrincipal;
+
+public class ConcurrentCreateUserTest extends AbstractConcurrencyTest {
+
+    /**
+     * The number of threads.
+     */
+    private static final int CONCURRENCY = 5;
+
+    List<String> userIDs = Collections.synchronizedList(new ArrayList<String>());
+    public static final String INTERMEDIATE_PATH = UUID.randomUUID().toString();
+
+    @Override
+    protected void tearDown() throws Exception {
+
+        try {
+            for (String id : userIDs) {
+                Authorizable a = ((JackrabbitSession)superuser).getUserManager().getAuthorizable(id);
+                a.remove();
+                superuser.save();
+            }
+        }
+        catch (Exception e) {
+            // this is best effort
+        }
+        
+        super.tearDown();
+    }
+
+    public void testCreateUsers() throws Exception {
+
+        log.println("ConcurrentCreateUserTest.testCreateUsers: c="
+                + CONCURRENCY);
+        log.flush();
+
+        runTask(new Task() {
+            public void execute(Session session, Node test)
+                    throws RepositoryException {
+                JackrabbitSession s = null;
+                try {
+                    s = (JackrabbitSession) getHelper().getSuperuserSession();
+                    String name = "newname-" + UUID.randomUUID();
+                    Authorizable authorizable = s.getUserManager().createUser(
+                            name, "password1", new TestPrincipal(name),
+                            INTERMEDIATE_PATH);
+                    s.save();
+                    userIDs.add(authorizable.getID());
+                    log.println(authorizable + " created");
+                } finally {
+                    s.logout();
+                }
+            }
+        }, CONCURRENCY, "/" + testPath);
+    }
+}

Property changes on: jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/ConcurrentCreateUserTest.java
___________________________________________________________________
Added: svn:executable
   + *

Index: jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/TestAll.java
===================================================================
--- jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/TestAll.java	(revision 1176331)
+++ jackrabbit-core/src/test/java/org/apache/jackrabbit/api/security/user/TestAll.java	(working copy)
@@ -42,6 +42,7 @@
         suite.addTestSuite(NestedGroupTest.class);
         suite.addTestSuite(ImpersonationTest.class);
         suite.addTestSuite(UserManagerSearchTest.class);
+        suite.addTestSuite(ConcurrentCreateUserTest.class);
 
         return suite;
     }
Index: jackrabbit-core/src/main/java/org/apache/jackrabbit/core/security/user/UserManagerImpl.java
===================================================================
--- jackrabbit-core/src/main/java/org/apache/jackrabbit/core/security/user/UserManagerImpl.java	(revision 1176331)
+++ jackrabbit-core/src/main/java/org/apache/jackrabbit/core/security/user/UserManagerImpl.java	(working copy)
@@ -57,6 +57,7 @@
 import java.util.Properties;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.Semaphore;
 
 /**
  * Default implementation of the <code>UserManager</code> interface with the
@@ -258,6 +259,12 @@
 
     private final MembershipCache membershipCache;
 
+    // allow only one user creation operation at a time in order to avoid
+    // race conditions when creating intermediate paths
+    private static Semaphore USERCREATIONSEM = new Semaphore(1);
+    // see above
+    private static Semaphore GROUPCREATIONSEM = new Semaphore(1);
+
     /**
      * Create a new <code>UserManager</code> with the default configuration.
      *
@@ -530,6 +537,7 @@
         // NOTE: principal validation during setPrincipal call.
 
         try {
+            USERCREATIONSEM.acquireUninterruptibly();
             NodeImpl userNode = (NodeImpl) nodeCreator.createUserNode(userID, intermediatePath);
             setPrincipal(userNode, principal);
             setProperty(userNode, P_PASSWORD, getValue(UserImpl.buildPasswordValue(password)), true);
@@ -547,6 +555,10 @@
             log.debug("Failed to create new User, reverting changes.");
             throw e;
         }
+        finally {
+            USERCREATIONSEM.release();
+        }
+        
     }
 
     /**
@@ -609,6 +621,7 @@
         checkValidID(groupID);
         // NOTE: principal validation during setPrincipal call.
         try {
+            GROUPCREATIONSEM.acquireUninterruptibly();
             NodeImpl groupNode = (NodeImpl) nodeCreator.createGroupNode(groupID, intermediatePath);
             
             if (principal != null) {
@@ -627,6 +640,9 @@
             log.debug("newInstance new Group failed, revert changes on parent");
             throw e;
         }
+        finally {
+            GROUPCREATIONSEM.release();
+        }
     }
 
     /**