Change: Lock table for each auto-deleted report individually

The auto_delete_reports function no longer keeps the access exclusive
lock on the reports table for the entire loop over the reports, but
instead acquires and releases the lock for each report to delete.

This gives other processes, like ones deleting reports manually, a
better chance to acquire the lock on the reports table.

src/manage_sql.c

@@ -18917,15 +18917,7 @@ auto_delete_reports ()
 
   g_debug ("%s", __func__);
 
-  sql_begin_immediate ();
-
-  /* As in delete_report, this prevents other processes from getting the
-   * report ID. */
-  if (sql_int ("SELECT try_exclusive_lock('reports');") == 0)
-    {
-      sql_rollback ();
-      return;
-    }
+  GArray *reports_to_delete = g_array_new (TRUE, TRUE, sizeof(report_t));
 
   init_iterator (&tasks,
                  "SELECT id, name,"
@@ -18970,31 +18962,64 @@ auto_delete_reports ()
                      keep);
       while (next (&reports))
         {
-          int ret;
           report_t report;
 
           report = iterator_int64 (&reports, 0);
           assert (report);
 
-          g_debug ("%s: delete %llu", __func__, report);
-          ret = delete_report_internal (report);
-          if (ret == 2)
-            {
-              /* Report is in use. */
-              g_debug ("%s: %llu is in use", __func__, report);
-              continue;
-            }
-          if (ret)
-            {
-              g_warning ("%s: failed to delete %llu (%i)",
-                         __func__, report, ret);
-              sql_rollback ();
-            }
+          g_debug ("%s: %llu to be deleted", __func__, report);
+
+          g_array_append_val (reports_to_delete, report);
         }
       cleanup_iterator (&reports);
     }
   cleanup_iterator (&tasks);
-  sql_commit ();
+
+  for (int i = 0; i < reports_to_delete->len; i++)
+    {
+      int ret;
+      report_t report = g_array_index (reports_to_delete, report_t, i);
+
+      sql_begin_immediate ();
+
+      /* As in delete_report, this prevents other processes from getting the
+       * report ID. */
+      if (sql_int ("SELECT try_exclusive_lock('reports');") == 0)
+        {
+          g_debug ("%s: could not acquire lock on reports table", __func__);
+          sql_rollback ();
+          g_array_free (reports_to_delete, TRUE);
+          return;
+        }
+
+      /* Check if report still exists in case another process has deleted it
+       *  in the meantime. */
+      if (sql_int ("SELECT count(*) FROM reports WHERE id = %llu",
+                    report) == 0)
+        {
+          g_debug ("%s: %llu no longer exists", __func__, report);
+          sql_rollback ();
+          continue;
+        }
+
+      g_debug ("%s: deleting report %llu", __func__, report);
+      ret = delete_report_internal (report);
+      if (ret == 2)
+        {
+          /* Report is in use. */
+          g_debug ("%s: %llu is in use", __func__, report);
+          continue;
+        }
+      if (ret)
+        {
+          g_warning ("%s: failed to delete %llu (%i)",
+                      __func__, report, ret);
+          sql_rollback ();
+          continue;
+        }
+      sql_commit ();
+    }
+  g_array_free (reports_to_delete, TRUE);
 }