feat: add BigtableDataClientFactory to create lightweight data clients (#112)

* feat: add BigtableDataClientFactory to create lightweight data clients

The new factory allows users to construct a single heavy factory object that can create many lightweight clients.
This is meant to be used in situations when a single application needs to access multiple instances or use different application profiles

* code format

* disclaimer comment

Author: igorbernstein2

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/BigtableDataClientFactory.java

@@ -0,0 +1,204 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.cloud.bigtable.data.v2;
+
+import com.google.api.core.BetaApi;
+import com.google.api.gax.core.BackgroundResource;
+import com.google.api.gax.core.FixedCredentialsProvider;
+import com.google.api.gax.core.FixedExecutorProvider;
+import com.google.api.gax.rpc.ClientContext;
+import com.google.api.gax.rpc.FixedHeaderProvider;
+import com.google.api.gax.rpc.FixedTransportChannelProvider;
+import com.google.api.gax.rpc.FixedWatchdogProvider;
+import com.google.api.gax.rpc.StubSettings;
+import java.io.IOException;
+import javax.annotation.Nonnull;
+
+/**
+ * A factory to create multiple {@link BigtableDataClient} instances that all share the same channel
+ * pool.
+ *
+ * <p>This allows multiple client instances to share the same gRPC channel pool, which makes client
+ * creation very cheap. The intended use case is for applications that need to access multiple
+ * Bigtable Instances from the same process.
+ *
+ * <p>Example Usage:
+ *
+ * <pre>{@code
+ * BigtableDataSettings defaultSettings = BigtableDataSettings.newBuilder()
+ *   .setProject("my-default-project")
+ *   .setInstance("my-default-instance")
+ *   .build();
+ *
+ * BigtableDataClientFactory clientFactory = BigtableDataClientFactory.create(defaultSettings);
+ *
+ * // Create a new client for "my-default-instance" in "my-default-project";
+ * BigtableDataClient defaultInstanceClient = clientFactory.createDefault();
+ *
+ * // Create a new client for a different application profile
+ * BigtableDataClient otherAppProfileClient = clientFactory.createForAppProfile("other-app-profile");
+ *
+ * // Create a new client for a completely different instance and application profile.
+ * BigtableDataClient otherInstanceClient = clientFactory
+ *   .createForInstance("my-other-project", "my-other-instance", "my-other-app-profile");
+ *
+ * // Clean up: make sure close the clients AND the factory.
+ * defaultInstanceClient.close();
+ * otherAppProfileClient.close();
+ * otherInstanceClient.close();
+ *
+ * clientFactory.close();
+ *
+ * <p>Please note that this is an experimental feature and might be changed or removed in future.
+ * }</pre>
+ */
+@BetaApi("This feature is currently experimental and can change in the future")
+public final class BigtableDataClientFactory implements AutoCloseable {
+  private final BigtableDataSettings defaultSettings;
+  private final ClientContext sharedClientContext;
+
+  /**
+   * Create a instance of this factory.
+   *
+   * <p>The factory will be used to create clients using the provided settings as the base. Make
+   * sure to call {@link #close()} on the factory after closing all clients.
+   */
+  public static BigtableDataClientFactory create(BigtableDataSettings defaultSettings)
+      throws IOException {
+    ClientContext sharedClientContext = ClientContext.create(defaultSettings.getStubSettings());
+    return new BigtableDataClientFactory(sharedClientContext, defaultSettings);
+  }
+
+  private BigtableDataClientFactory(
+      ClientContext sharedClientContext, BigtableDataSettings defaultSettings) {
+    this.sharedClientContext = sharedClientContext;
+    this.defaultSettings = defaultSettings;
+  }
+
+  /**
+   * Release all of the resources associated with this factory.
+   *
+   * <p>This will close the underlying channel pooling, disconnecting all create clients.
+   */
+  @Override
+  public void close() throws Exception {
+    for (BackgroundResource resource : sharedClientContext.getBackgroundResources()) {
+      resource.close();
+    }
+  }
+
+  /**
+   * Create a lightweight client using the default settings in this factory. This will use the
+   * factory default project, instance and application profile ids. The client will also share
+   * resources like the channel pool with other clients created using this factory.
+   *
+   * <p>The client should be closed when it is no longer needed. Closing the client will release
+   * client specific resources, but will leave shared resources like the channel pool open. To
+   * release all resources, first close all of the created clients and then this factory instance.
+   */
+  public BigtableDataClient createDefault() {
+    BigtableDataSettings.Builder settingsBuilder = defaultSettings.toBuilder();
+    patchStubSettings(settingsBuilder.stubSettings());
+    BigtableDataSettings settings = settingsBuilder.build();
+
+    try {
+      return BigtableDataClient.create(settings);
+    } catch (IOException e) {
+      // Should never happen because the connection has been established already
+      throw new RuntimeException(
+          "Failed to create a new client using factory default settings and shared resources.");
+    }
+  }
+
+  /**
+   * Create a lightweight client with an overriden application profile and the factory default
+   * project and instance ids. The client will also share resources like the channel pool with other
+   * clients created using this factory.
+   *
+   * <p>The client should be closed when it is no longer needed. Closing the client will release
+   * client specific resources, but will leave shared resources like the channel pool open. To
+   * release all resources, first close all of the created clients and then this factory instance.
+   */
+  public BigtableDataClient createForAppProfile(@Nonnull String appProfileId) throws IOException {
+    BigtableDataSettings.Builder settingsBuilder =
+        defaultSettings.toBuilder().setAppProfileId(appProfileId);
+
+    patchStubSettings(settingsBuilder.stubSettings());
+
+    return BigtableDataClient.create(settingsBuilder.build());
+  }
+
+  /**
+   * Create a lightweight client with the specified project and instance id. The resulting client
+   * will use the server default application profile. The client will also share resources like the
+   * channel pool with other clients created using this factory.
+   *
+   * <p>The client should be closed when it is no longer needed. Closing the client will release
+   * client specific resources, but will leave shared resources like the channel pool open. To
+   * release all resources, first close all of the created clients and then this factory instance.
+   */
+  public BigtableDataClient createForInstance(@Nonnull String projectId, @Nonnull String instanceId)
+      throws IOException {
+    BigtableDataSettings.Builder settingsBuilder =
+        defaultSettings
+            .toBuilder()
+            .setProjectId(projectId)
+            .setInstanceId(instanceId)
+            .setDefaultAppProfileId();
+
+    patchStubSettings(settingsBuilder.stubSettings());
+
+    return BigtableDataClient.create(settingsBuilder.build());
+  }
+
+  /**
+   * Create a lightweight client to the specified project, instance and application profile id. The
+   * client will share resources like the channel pool with other clients created using this
+   * factory.
+   *
+   * <p>The client should be closed when it is no longer needed. Closing the client will release
+   * client specific resources, but will leave shared resources like the channel pool open. To
+   * release all resources, first close all of the created clients and then this factory instance.
+   */
+  public BigtableDataClient createForInstance(
+      @Nonnull String projectId, @Nonnull String instanceId, @Nonnull String appProfileId)
+      throws IOException {
+    BigtableDataSettings.Builder settingsBuilder =
+        defaultSettings
+            .toBuilder()
+            .setProjectId(projectId)
+            .setInstanceId(instanceId)
+            .setAppProfileId(appProfileId);
+
+    patchStubSettings(settingsBuilder.stubSettings());
+
+    return BigtableDataClient.create(settingsBuilder.build());
+  }
+
+  // Update stub settings to use shared resources in this factory
+  private void patchStubSettings(StubSettings.Builder stubSettings) {
+    stubSettings
+        .setTransportChannelProvider(
+            FixedTransportChannelProvider.create(sharedClientContext.getTransportChannel()))
+        .setCredentialsProvider(
+            FixedCredentialsProvider.create(sharedClientContext.getCredentials()))
+        .setExecutorProvider(FixedExecutorProvider.create(sharedClientContext.getExecutor()))
+        .setStreamWatchdogProvider(
+            FixedWatchdogProvider.create(sharedClientContext.getStreamWatchdog()))
+        .setHeaderProvider(FixedHeaderProvider.create(sharedClientContext.getHeaders()))
+        .setClock(sharedClientContext.getClock());
+  }
+}

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/BigtableDataSettings.java

@@ -255,16 +255,34 @@ public String getInstanceId() {
     }
 
     /**
-     * Sets the AppProfile to use. An application profile (sometimes also shortened to "app
-     * profile") is a group of configuration parameters for an individual use case. A client will
-     * identify itself with an application profile ID at connection time, and the requests will be
-     * handled according to that application profile.
+     * Sets the AppProfile to use.
+     *
+     * <p>An application profile (sometimes also shortened to "app profile") is a group of
+     * configuration parameters for an individual use case. A client will identify itself with an
+     * application profile ID at connection time, and the requests will be handled according to that
+     * application profile.
      */
     public Builder setAppProfileId(@Nonnull String appProfileId) {
       stubSettings.setAppProfileId(appProfileId);
       return this;
     }
 
+    /**
+     * Resets the AppProfile id to the default for the instance.
+     *
+     * <p>An application profile (sometimes also shortened to "app profile") is a group of
+     * configuration parameters for an individual use case. A client will identify itself with an
+     * application profile ID at connection time, and the requests will be handled according to that
+     * application profile.
+     *
+     * <p>Every Bigtable Instance has a default application profile associated with it, this method
+     * configures the client to use it.
+     */
+    public Builder setDefaultAppProfileId() {
+      stubSettings.setDefaultAppProfileId();
+      return this;
+    }
+
     /** Gets the app profile id that was previously set on this Builder. */
     public String getAppProfileId() {
       return stubSettings.getAppProfileId();

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/EnhancedBigtableStubSettings.java

@@ -610,6 +610,22 @@ public Builder setAppProfileId(@Nonnull String appProfileId) {
       return this;
     }
 
+    /**
+     * Resets the AppProfile id to the default for the instance.
+     *
+     * <p>An application profile (sometimes also shortened to "app profile") is a group of
+     * configuration parameters for an individual use case. A client will identify itself with an
+     * application profile ID at connection time, and the requests will be handled according to that
+     * application profile.
+     *
+     * <p>Every Bigtable Instance has a default application profile associated with it, this method
+     * configures the client to use it.
+     */
+    public Builder setDefaultAppProfileId() {
+      setAppProfileId(SERVER_DEFAULT_APP_PROFILE_ID);
+      return this;
+    }
+
     /** Gets the app profile id that was previously set on this Builder. */
     public String getAppProfileId() {
       return appProfileId;