[FLINK-19435][connectors/jdbc] Fix deadlock when loading different sq…

…l driver classes concurrently using Class.forName This closes #14361
apache · Dec 21, 2020 · 84ed653 · 84ed653
1 parent 7ca2dd3
commit 84ed653
Show file tree

Hide file tree

Showing 4 changed files with 30 additions and 0 deletions.
diff --git a/...s/flink-connector-jdbc/src/main/java/org/apache/flink/connector/jdbc/JdbcInputFormat.java b/...s/flink-connector-jdbc/src/main/java/org/apache/flink/connector/jdbc/JdbcInputFormat.java
@@ -141,6 +141,12 @@ public void configure(Configuration parameters) {
 	public void openInputFormat() {
 		//called once per inputFormat (on open)
 		try {
+			// Load DriverManager first to avoid deadlock between DriverManager's
+			// static initialization block and specific driver class's static
+			// initialization block.
+			//
+			// See comments in SimpleJdbcConnectionProvider for more details.
+			DriverManager.getDrivers();
 			Class.forName(drivername);
 			if (username == null) {
 				dbConn = DriverManager.getConnection(dbURL);

diff --git a/...ava/org/apache/flink/connector/jdbc/internal/connection/SimpleJdbcConnectionProvider.java b/...ava/org/apache/flink/connector/jdbc/internal/connection/SimpleJdbcConnectionProvider.java
@@ -40,6 +40,18 @@ public class SimpleJdbcConnectionProvider implements JdbcConnectionProvider, Ser
 
 	private transient volatile Connection connection;
 
+	static {
+		// Load DriverManager first to avoid deadlock between DriverManager's
+		// static initialization block and specific driver class's static
+		// initialization block when two different driver classes are loading
+		// concurrently using Class.forName while DriverManager is uninitialized
+		// before.
+		//
+		// This could happen in JDK 8 but not above as driver loading has been
+		// moved out of DriverManager's static initialization block since JDK 9.
+		DriverManager.getDrivers();
+	}
+
 	public SimpleJdbcConnectionProvider(JdbcConnectionOptions jdbcOptions) {
 		this.jdbcOptions = jdbcOptions;
 	}

diff --git a/...onnector-jdbc/src/main/java/org/apache/flink/connector/jdbc/table/JdbcLookupFunction.java b/...onnector-jdbc/src/main/java/org/apache/flink/connector/jdbc/table/JdbcLookupFunction.java
@@ -205,6 +205,12 @@ private Row convertToRowFromResultSet(ResultSet resultSet) throws SQLException {
 	}
 
 	private void establishConnectionAndStatement() throws SQLException, ClassNotFoundException {
+		// Load DriverManager first to avoid deadlock between DriverManager's
+		// static initialization block and specific driver class's static
+		// initialization block.
+		//
+		// See comments in SimpleJdbcConnectionProvider for more details.
+		DriverManager.getDrivers();
 		Class.forName(drivername);
 		if (username == null) {
 			dbConn = DriverManager.getConnection(dbURL);

diff --git a/...r-jdbc/src/main/java/org/apache/flink/connector/jdbc/table/JdbcRowDataLookupFunction.java b/...r-jdbc/src/main/java/org/apache/flink/connector/jdbc/table/JdbcRowDataLookupFunction.java
@@ -195,6 +195,12 @@ public void eval(Object... keys) {
 	}
 
 	private void establishConnectionAndStatement() throws SQLException, ClassNotFoundException {
+		// Load DriverManager first to avoid deadlock between DriverManager's
+		// static initialization block and specific driver class's static
+		// initialization block.
+		//
+		// See comments in SimpleJdbcConnectionProvider for more details.
+		DriverManager.getDrivers();
 		Class.forName(drivername);
 		if (username == null) {
 			dbConn = DriverManager.getConnection(dbURL);