feat: add shutdown() to ConnectorRegistry

alloydb-jdbc-connector/src/main/java/com/google/cloud/alloydb/ConnectorRegistry.java

@@ -45,4 +45,12 @@ public static void close(String name) {
   public static void reset() {
     InternalConnectorRegistry.INSTANCE.resetInstance();
   }
+
+  /**
+   * Shutdown the entire AlloyDB JDBC Connector. This will stop all background threads. All future
+   * attempts to connect to the database will fail.
+   */
+  public static void shutdown() {
+    InternalConnectorRegistry.INSTANCE.shutdownInstance();
+  }
 }

alloydb-jdbc-connector/src/main/java/com/google/cloud/alloydb/InternalConnectorRegistry.java

@@ -44,6 +44,9 @@ enum InternalConnectorRegistry implements Closeable {
   @SuppressWarnings("ImmutableEnumChecker")
   private ConcurrentHashMap<String, Connector> namedConnectors;
 
+  @SuppressWarnings("ImmutableEnumChecker")
+  private boolean shutdown = false;
+
   InternalConnectorRegistry() {
     // During refresh, each instance consumes 2 threads from the thread pool. By using 8 threads,
     // there should be enough free threads so that there will not be a deadlock. Most users
@@ -63,6 +66,10 @@ enum InternalConnectorRegistry implements Closeable {
    * @throws IOException if error occurs during socket creation.
    */
   public Socket connect(ConnectionConfig config) throws IOException {
+    if (shutdown) {
+      throw new IllegalStateException("ConnectorRegistry was shut down.");
+    }
+
     if (config.getNamedConnector() != null) {
       Connector connector = getNamedConnector(config.getNamedConnector());
       return connector.connect(config.withConnectorConfig(connector.getConfig()));
@@ -79,6 +86,10 @@ public Socket connect(ConnectionConfig config) throws IOException {
 
   /** Register the configuration for a named connector. */
   public void register(String name, ConnectorConfig config) {
+    if (shutdown) {
+      throw new IllegalStateException("ConnectorRegistry was shut down.");
+    }
+
     if (this.namedConnectors.containsKey(name)) {
       throw new IllegalArgumentException("Named connection " + name + " exists.");
     }
@@ -87,15 +98,19 @@ public void register(String name, ConnectorConfig config) {
 
   /** Close a named connector, stopping the refresh process and removing it from the registry. */
   public void close(String name) {
+    if (shutdown) {
+      throw new IllegalStateException("ConnectorRegistry was shut down.");
+    }
+
     Connector connector = namedConnectors.remove(name);
     if (connector == null) {
       throw new IllegalArgumentException("Named connection " + name + " does not exist.");
     }
     connector.close();
   }
 
-  /** Shutdown all connectors and remove the singleton instance. */
-  private void shutdown() {
+  /** Shutdown all connectors. */
+  private void shutdownConnectors() {
     this.unnamedConnectors.forEach((key, c) -> c.close());
     this.unnamedConnectors.clear();
     this.namedConnectors.forEach((key, c) -> c.close());
@@ -104,13 +119,19 @@ private void shutdown() {
 
   @Override
   public void close() {
-    shutdown();
-    this.executor.shutdown();
+    shutdownInstance();
   }
 
   /** Calls shutdown on the singleton. */
   public void resetInstance() {
-    shutdown();
+    shutdownConnectors();
+  }
+
+  /** Calls shutdown on the singleton. */
+  public void shutdownInstance() {
+    shutdown = true;
+    shutdownConnectors();
+    this.executor.shutdown();
   }
 
   private Connector getConnector(ConnectionConfig config) {

docs/configuration.md

@@ -182,9 +182,21 @@ ConnectorRegistry.reset();
 ```
 
 After calling `ConnectorRegistry.reset()`, the next attempt to connect to a
-database using a SocketFactory or R2DBC ConnectionFactory, or
-to `ConnectorRegistry.register()` will start a new connector registry, restart
-the background threads, and create a new connector.
+database, or to `ConnectorRegistry.register()` will start a new connector
+registry, restart the background threads, and create a new connector.
+
+### Shutdown The Connector Registry
+
+The application may shut down the ConnectorRegistry. This closes all existing
+named and unnamed connectors, and stops internal background threads.
+
+```java
+ConnectorRegistry.shutdown();
+```
+
+After calling `ConnectorRegistry.shutdown()`, subsequent attempts to connect to
+a database, or to `ConnectorRegistry.register()` will fail, 
+throwing `IllegalStateException`.
 
 ## Configuring Google Credentials