Fixes deadlock in dhcp ip assignment logic caused by nesting calls to distributed primitives.

Change-Id: I25acd37cbf3800ad260c672c99e9f630435f0f88

@@ -25,13 +25,11 @@ import org.apache.felix.scr.annotations.Service;
 import org.onlab.packet.Ip4Address;
 import org.onlab.packet.MacAddress;
 import org.onlab.util.KryoNamespace;
-import org.onlab.util.Tools;
 import org.onosproject.dhcp.DhcpStore;
 import org.onosproject.dhcp.IpAssignment;
 import org.onosproject.net.HostId;
 import org.onosproject.store.serializers.KryoNamespaces;
 import org.onosproject.store.service.ConsistentMap;
-import org.onosproject.store.service.ConsistentMapException;
 import org.onosproject.store.service.DistributedSet;
 import org.onosproject.store.service.Serializer;
 import org.onosproject.store.service.StorageService;
@@ -44,7 +42,6 @@ import java.util.Map;
 import java.util.List;
 import java.util.HashMap;
 import java.util.Objects;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * Manages the pool of available IP Addresses in the network and
@@ -172,15 +169,11 @@ public class DistributedDhcpStore implements DhcpStore {
                             List<Ip4Address> addressList) {
         log.debug("Assign IP Called w/ Ip4Address: {}, HostId: {}", ipAddr.toString(), hostId.mac().toString());
 
-        AtomicBoolean assigned = Tools.retryable(() -> {
-            AtomicBoolean result = new AtomicBoolean(false);
-            allocationMap.compute(
-                    hostId,
-                    (h, existingAssignment) -> {
-                        IpAssignment assignment = existingAssignment;
-                        if (existingAssignment == null) {
+        Versioned<IpAssignment> currentAssignment = allocationMap.get(hostId);
+        IpAssignment newAssignment = null;
+        if (currentAssignment == null) {
             if (rangeNotEnforced) {
-                                assignment = IpAssignment.builder()
+                newAssignment = IpAssignment.builder()
                         .ipAddress(ipAddr)
                         .timestamp(new Date())
                         .leasePeriod(leaseTime)
@@ -191,21 +184,26 @@ public class DistributedDhcpStore implements DhcpStore {
                         .routerAddress((Ip4Address) addressList.toArray()[2])
                         .domainServer((Ip4Address) addressList.toArray()[3])
                         .build();
-                                result.set(true);
+
             } else if (freeIPPool.remove(ipAddr)) {
-                                assignment = IpAssignment.builder()
+                newAssignment = IpAssignment.builder()
                         .ipAddress(ipAddr)
                         .timestamp(new Date())
                         .leasePeriod(leaseTime)
                         .assignmentStatus(IpAssignment.AssignmentStatus.Option_Assigned)
                         .build();
-                                result.set(true);
+            } else {
+                return false;
             }
-                        } else if (Objects.equals(existingAssignment.ipAddress(), ipAddr) &&
+            return allocationMap.putIfAbsent(hostId, newAssignment) == null;
+            // TODO: handle the case where map changed.
+        } else {
+            IpAssignment existingAssignment = currentAssignment.value();
+            if (Objects.equals(existingAssignment.ipAddress(), ipAddr) &&
                     (existingAssignment.rangeNotEnforced() || ipWithinRange(ipAddr))) {
                 switch (existingAssignment.assignmentStatus()) {
                     case Option_RangeNotEnforced:
-                                    assignment = IpAssignment.builder()
+                        newAssignment = IpAssignment.builder()
                                 .ipAddress(ipAddr)
                                 .timestamp(new Date())
                                 .leasePeriod(existingAssignment.leasePeriod())
@@ -216,39 +214,34 @@ public class DistributedDhcpStore implements DhcpStore {
                                 .routerAddress(existingAssignment.routerAddress())
                                 .domainServer(existingAssignment.domainServer())
                                 .build();
-                                    result.set(true);
                         break;
                     case Option_Assigned:
                     case Option_Requested:
-                                    assignment = IpAssignment.builder()
+                        newAssignment = IpAssignment.builder()
                                 .ipAddress(ipAddr)
                                 .timestamp(new Date())
                                 .leasePeriod(leaseTime)
                                 .assignmentStatus(IpAssignment.AssignmentStatus.Option_Assigned)
                                 .build();
-                                    result.set(true);
                         break;
                     case Option_Expired:
                         if (freeIPPool.remove(ipAddr)) {
-                                        assignment = IpAssignment.builder()
+                            newAssignment = IpAssignment.builder()
                                     .ipAddress(ipAddr)
                                     .timestamp(new Date())
                                     .leasePeriod(leaseTime)
                                     .assignmentStatus(IpAssignment.AssignmentStatus.Option_Assigned)
                                     .build();
-                                        result.set(true);
                         }
                         break;
                     default:
                         break;
                 }
+                return allocationMap.replace(hostId, currentAssignment.version(), newAssignment);
+            } else {
+                return false;
+            }
         }
-                        return assignment;
-                    });
-            return result;
-        }, ConsistentMapException.class, MAX_RETRIES, MAX_BACKOFF).get();
-
-        return assigned.get();
     }
 
     @Override