[CALCITE-5841] Improve singleton implementation for `ChinookAvaticaSe…

…rver` in calcite-plus Close apache#3313
asolimando · Jul 29, 2023 · e3310c2 · e3310c2
1 parent 11126c5
commit e3310c2
Showing 1 changed file with 19 additions and 14 deletions.
diff --git a/plus/src/main/java/org/apache/calcite/chinook/ChinookAvaticaServer.java b/plus/src/main/java/org/apache/calcite/chinook/ChinookAvaticaServer.java
@@ -62,16 +62,18 @@ public static class CalciteChinookMetaFactory implements Meta.Factory {
     private static final CalciteConnectionProvider CONNECTION_PROVIDER =
         new CalciteConnectionProvider();
 
-    private static JdbcMeta instance = null;
+    private static volatile JdbcMeta instance = null;
 
     private static JdbcMeta getInstance() {
       if (instance == null) {
-        try {
-          instance =
-              new JdbcMeta(CalciteConnectionProvider.DRIVER_URL,
-                  CONNECTION_PROVIDER.provideConnectionInfo());
-        } catch (SQLException | IOException e) {
-          throw new RuntimeException(e);
+        synchronized (CalciteChinookMetaFactory.class) {
+          try {
+            instance =
+                new JdbcMeta(CalciteConnectionProvider.DRIVER_URL,
+                    CONNECTION_PROVIDER.provideConnectionInfo());
+          } catch (SQLException | IOException e) {
+            throw new RuntimeException(e);
+          }
         }
       }
       return instance;
@@ -86,16 +88,19 @@ private static JdbcMeta getInstance() {
    * Factory for Chinook Calcite database wrapped in meta for Avatica.
    */
   public static class RawChinookMetaFactory implements Meta.Factory {
-    private static JdbcMeta instance = null;
+    private static volatile JdbcMeta instance = null;
 
     private static JdbcMeta getInstance() {
       if (instance == null) {
-        try {
-          instance =
-              new JdbcMeta(ChinookHsqldb.URI,
-                  ChinookHsqldb.USER, ChinookHsqldb.PASSWORD);
-        } catch (SQLException e) {
-          throw new RuntimeException(e);
+        synchronized (RawChinookMetaFactory.class) {
+          if (instance == null) {
+            try {
+              instance =
+                  new JdbcMeta(ChinookHsqldb.URI, ChinookHsqldb.USER, ChinookHsqldb.PASSWORD);
+            } catch (SQLException e) {
+              throw new RuntimeException(e);
+            }
+          }
         }
       }
       return instance;