Fixed pgAdmin freezing issue by providing the error message for the operation

that can't perform due to lock on the particular table. Fixes #5427

docs/en_US/release_notes_6_2.rst

@@ -18,6 +18,7 @@ Housekeeping
 Bug fixes
 *********
 
+| `Issue #5427 <https://redmine.postgresql.org/issues/5427>`_ -  Fixed pgAdmin freezing issue by providing the error message for the operation that can't perform due to lock on the particular table.
 | `Issue #6780 <https://redmine.postgresql.org/issues/6780>`_ -  Ensure that columns should be merged if the newly added column is present in the parent table.
 | `Issue #6859 <https://redmine.postgresql.org/issues/6859>`_ -  Fixed an issue where properties panel is not updated when any object is added from the browser tree.
 | `Issue #6949 <https://redmine.postgresql.org/issues/6949>`_ -  Ensure that dialog should be opened when clicking on Reassign/Drop owned menu.

web/pgadmin/browser/server_groups/servers/databases/schemas/tables/__init__.py

@@ -1070,6 +1070,10 @@ class TableView(BaseTableView, DataTypeReader, SchemaDiffTableCompare):
                         )
                     )
 
+                lock_on_table = self.get_table_locks(did, res['rows'][0])
+                if lock_on_table != '':
+                    return lock_on_table
+
                 status, res = super(TableView, self).delete(gid, sid, did,
                                                             scid, tid, res)
 

web/pgadmin/browser/server_groups/servers/databases/schemas/tables/static/js/table.js

@@ -205,6 +205,9 @@ define('pgadmin.node.table', [
                         t.select(i);
                       }, 10);
                     }
+                    if (res.success == 2) {
+                      Alertify.error(res.info, 0);
+                    }
                   })
                   .fail(function(xhr, status, error) {
                     Alertify.pgRespErrorNotify(xhr, error);

web/pgadmin/browser/server_groups/servers/databases/schemas/tables/templates/tables/sql/default/get_application_name.sql

@@ -0,0 +1,8 @@
+SELECT
+    usename,
+    application_name
+FROM
+    pg_catalog.pg_stat_activity
+WHERE
+    pid =  {{ pid }}
+ORDER BY pid

web/pgadmin/browser/server_groups/servers/databases/schemas/tables/templates/tables/sql/default/locks.sql

@@ -0,0 +1,23 @@
+SELECT
+    pid,
+    locktype,
+    datname,
+    relation::regclass,
+    page,
+    tuple,
+    virtualxid
+    transactionid,
+    classid::regclass,
+    objid,
+    objsubid,
+    virtualtransaction,
+    mode,
+    granted,
+    fastpath
+FROM
+    pg_catalog.pg_locks l
+    LEFT OUTER JOIN pg_catalog.pg_database d ON (l.database = d.oid)
+{% if did %}WHERE
+    datname = (SELECT datname FROM pg_catalog.pg_database WHERE oid = {{ did }}){% endif %}
+ORDER BY
+    pid, locktype

web/pgadmin/browser/server_groups/servers/databases/schemas/tables/utils.py

@@ -49,6 +49,7 @@ from pgadmin.utils.preferences import Preferences
 from pgadmin.browser.server_groups.servers.databases.schemas.utils \
     import VacuumSettings
 from pgadmin.tools.schema_diff.node_registry import SchemaDiffRegistry
+from pgadmin.dashboard import locks
 
 
 class BaseTableView(PGChildNodeView, BasePartitionTable, VacuumSettings):
@@ -1952,6 +1953,10 @@ class BaseTableView(PGChildNodeView, BasePartitionTable, VacuumSettings):
 
         data = res['rows'][0]
 
+        lock_on_table = self.get_table_locks(did, data)
+        if lock_on_table != '':
+            return lock_on_table
+
         sql = render_template("/".join([self.table_template_path,
                                         'truncate.sql']),
                               data=data, cascade=is_cascade,
@@ -2004,6 +2009,41 @@ class BaseTableView(PGChildNodeView, BasePartitionTable, VacuumSettings):
             'scid': scid
         }
 
+    def get_table_locks(self, did, data):
+        """
+        This function returns the lock details if there is any on table
+        :param did:
+        :param data:
+        :return:
+        """
+        sql = render_template(
+            "/".join([self.table_template_path, 'locks.sql']), did=did
+        )
+        status, lock_table_result = self.conn.execute_dict(sql)
+
+        for row in lock_table_result['rows']:
+            if row['relation'].strip('\"') == data['name']:
+
+                sql = render_template(
+                    "/".join([self.table_template_path,
+                              'get_application_name.sql']), pid=row['pid']
+                )
+                status, res = self.conn.execute_dict(sql)
+
+                application_name = res['rows'][0]['application_name']
+
+                return make_json_response(
+                    success=2,
+                    info=gettext(
+                        "The table is currently locked and the "
+                        "operation cannot be completed. "
+                        "Please try again later. "
+                        "\r\nBlocking Process ID : {0} "
+                        "Application Name : {1}").format(row['pid'],
+                                                         application_name)
+                )
+        return ''
+
     def get_schema_and_table_name(self, tid):
         """
         This function will fetch the schema qualified name of the

web/pgadmin/browser/static/js/node.js

@@ -838,6 +838,10 @@ define('pgadmin.browser.node', [
               type: 'DELETE',
             })
               .done(function(res) {
+                if(res.success == 2){
+                  Alertify.error(res.info, 0);
+                  return;
+                }
                 if (res.success == 0) {
                   pgBrowser.report_error(res.errormsg, res.info);
                 } else {
@@ -867,7 +871,6 @@ define('pgadmin.browser.node', [
                 }
                 pgBrowser.report_error(
                   gettext('Error dropping/removing %s: "%s"', obj.label, objName), errmsg);
-
               });
           },
           null