Fixed data race on creation of cached contexts

Author: alex268

jdbc/src/main/java/tech/ydb/jdbc/YdbDriver.java

@@ -77,9 +77,10 @@ public YdbContext getCachedContext(YdbConfig config) throws SQLException {
         }
 
         context = YdbContext.createContext(config);
-        YdbContext old = cache.put(config, context);
+        YdbContext old = cache.putIfAbsent(config, context);
         if (old != null) {
-            old.close();
+            context.close();
+            return old;
         }
         return context;
     }

jdbc/src/test/java/tech/ydb/jdbc/YdbDriverIntegrationTest.java

@@ -4,8 +4,11 @@
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.util.ArrayDeque;
+import java.util.ArrayList;
 import java.util.Deque;
+import java.util.List;
 import java.util.Properties;
+import java.util.concurrent.CompletableFuture;
 
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
@@ -98,6 +101,29 @@ public void testContextCache() throws SQLException {
         }
     }
 
+    @Test
+    public void testContextCacheConncurrent() throws SQLException {
+        List<CompletableFuture<YdbContext>> list = new ArrayList<>();
+
+        for (int idx = 0; idx < 20; idx++) {
+            list.add(CompletableFuture.supplyAsync(() -> {
+                try (Connection conn1 = DriverManager.getConnection(jdbcURL.build())) {
+                    YdbConnection unwrapped = conn1.unwrap(YdbConnection.class);
+                    Assertions.assertNotNull(unwrapped.getCtx());
+                    return unwrapped.getCtx();
+                } catch (SQLException ex) {
+                    throw new RuntimeException("Cannot connect", ex);
+                }
+            }));
+        }
+
+        YdbContext first = list.get(0).join();
+
+        for (CompletableFuture<YdbContext> future: list) {
+            Assertions.assertEquals(first, future.join());
+        }
+    }
+
     @Test
     public void testResizeSessionPool() throws SQLException {
         String url = jdbcURL.build();