feat(server): support single computer do schedule task

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/task/DistributedTaskScheduler.java

@@ -441,7 +441,7 @@ public void waitUntilAllTasksCompleted(long seconds)
 
     @Override
     public void checkRequirement(String op) {
-        if (!this.serverManager().selfIsMaster()) {
+        if (!this.serverManager().selfIsMasterOrSingleComputer()) {
             throw new HugeException("Can't %s task on non-master server", op);
         }
     }

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/task/ServerInfoManager.java

@@ -172,8 +172,18 @@ public NodeRole selfNodeRole() {
         return this.globalNodeInfo.nodeRole();
     }
 
-    public boolean selfIsMaster() {
-        return this.selfNodeRole() != null && this.selfNodeRole().master();
+    public boolean selfIsMasterOrSingleComputer() {
+        boolean isMaster=this.selfNodeRole() != null && this.selfNodeRole().master();
+        boolean isSingleComputer=isStandAloneComputer();
+        return isMaster||isSingleComputer;
+    }
+
+    public boolean selfIsComputer() {
+        return this.selfNodeRole() != null && this.selfNodeRole().computer();
+    }
+
+    public boolean isStandAloneComputer(){
+        return this.onlySingleNode() && this.selfIsComputer();
     }
 
     public boolean onlySingleNode() {
@@ -198,7 +208,7 @@ public synchronized void heartbeat() {
             LOG.info("ServerInfo is missing: {}, may not be initialized yet", this.selfNodeId());
             return;
         }
-        if (this.selfIsMaster()) {
+        if (this.selfIsMasterOrSingleComputer()) {
             // On the master node, just wait for ServerInfo re-init
             LOG.warn("ServerInfo is missing: {}, may be cleared before", this.selfNodeId());
             return;
@@ -228,6 +238,32 @@ protected boolean graphIsReady() {
         return !this.closed && this.graph.started() && this.graph.initialized();
     }
 
+    protected synchronized void updateIsSingleNode(){
+        Collection<HugeServerInfo> servers=this.allServerInfos();
+        boolean hasWorkerNode = false;
+        long now = DateUtil.now().getTime();
+        int computerNodeCount=0;
+
+        // Iterate servers to find suitable one
+        for (HugeServerInfo server : servers) {
+            if (!server.alive()) {
+                continue;
+            }
+            if (server.role().master()) {
+                continue;
+            }else if (server.role().computer()){
+                computerNodeCount++;
+            }
+            hasWorkerNode = true;
+        }
+
+        boolean singleNode = !hasWorkerNode||computerNodeCount==1;
+        if (singleNode != this.onlySingleNode) {
+            LOG.info("Switch only_single_node 02 to {}", singleNode);
+            this.onlySingleNode = singleNode;
+        }
+    }
+
     protected synchronized HugeServerInfo pickWorkerNode(Collection<HugeServerInfo> servers,
                                                          HugeTask<?> task) {
         HugeServerInfo master = null;

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/task/StandardTaskScheduler.java

@@ -273,7 +273,7 @@ public synchronized <V> void cancel(HugeTask<V> task) {
             // The task scheduled to workers, let the worker node to cancel
             this.save(task);
             assert task.server() != null : task;
-            assert this.serverManager().selfIsMaster();
+            assert this.serverManager().selfIsMasterOrSingleComputer();
             if (!task.server().equals(this.serverManager().selfNodeId())) {
                 /*
                  * Remove the task from memory if it's running on worker node,
@@ -312,7 +312,7 @@ protected synchronized void scheduleTasksOnMaster() {
                     continue;
                 }
 
-                if (!this.serverManager.selfIsMaster()) {
+                if (!this.serverManager.selfIsMasterOrSingleComputer()) {
                     return;
                 }
 
@@ -720,7 +720,7 @@ public <V> V call(Callable<V> callable) {
     }
 
     private void checkOnMasterNode(String op) {
-        if (!this.serverManager().selfIsMaster()) {
+        if (!this.serverManager().selfIsMasterOrSingleComputer()) {
             throw new HugeException("Can't %s task on non-master server", op);
         }
     }

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/task/TaskManager.java

@@ -439,14 +439,15 @@ private void scheduleOrExecuteJobForGraph(TaskScheduler scheduler) {
                 // Update server heartbeat
                 serverManager.heartbeat();
 
+                serverManager.updateIsSingleNode();
                 /*
                  * Master will schedule tasks to suitable servers.
                  * Note a Worker may become to a Master, so elected-Master also needs to
                  * execute tasks assigned by previous Master when enableRoleElected=true.
                  * However, when enableRoleElected=false, a Master is only set by the
                  * config assignment, assigned-Master always stays the same state.
                  */
-                if (serverManager.selfIsMaster()) {
+                if (serverManager.selfIsMasterOrSingleComputer()) {
                     standardTaskScheduler.scheduleTasksOnMaster();
                     if (!this.enableRoleElected && !serverManager.onlySingleNode()) {
                         // assigned-Master + non-single-node don't need to execute tasks