Bigtable: improve list tables spooler (googleapis#3639)

* Bigtable: improve list tables spooler

Avoid blocking the event loop. Previously the first page would be fetched
asynchronously, but all of the other pages would be fetched synchronously
which would block the grpc event loop. The new implementation uses future
chaining.

* update async test as well

* reformat

Author: igorbernstein2

google-cloud-clients/google-cloud-bigtable-admin/src/main/java/com/google/cloud/bigtable/admin/v2/BigtableTableAdminClient.java

@@ -15,6 +15,7 @@
  */
 package com.google.cloud.bigtable.admin.v2;
 
+import com.google.api.core.ApiAsyncFunction;
 import com.google.api.core.ApiFunction;
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutures;
@@ -27,6 +28,7 @@
 import com.google.bigtable.admin.v2.InstanceName;
 import com.google.bigtable.admin.v2.ListTablesRequest;
 import com.google.bigtable.admin.v2.TableName;
+import com.google.cloud.bigtable.admin.v2.BaseBigtableTableAdminClient.ListTablesPage;
 import com.google.cloud.bigtable.admin.v2.BaseBigtableTableAdminClient.ListTablesPagedResponse;
 import com.google.cloud.bigtable.admin.v2.models.ConsistencyToken;
 import com.google.cloud.bigtable.admin.v2.models.CreateTableRequest;
@@ -433,22 +435,65 @@ public ApiFuture<List<TableName>> listTablesAsync() {
     ListTablesRequest request = ListTablesRequest.newBuilder().setParent(instanceName.toString())
         .build();
 
-    ApiFuture<ListTablesPagedResponse> listResp =
-        this.stub.listTablesPagedCallable().futureCall(request);
+    // TODO(igorbernstein2): try to upstream pagination spooling or figure out a way to expose the
+    // paginated responses while maintaining the wrapper facade.
 
-    return ApiFutures.transform(
-        listResp,
-        new ApiFunction<ListTablesPagedResponse, List<TableName>>() {
+    // Fetch the first page.
+    ApiFuture<ListTablesPage> firstPageFuture = ApiFutures.transform(
+        stub.listTablesPagedCallable().futureCall(request),
+        new ApiFunction<ListTablesPagedResponse, ListTablesPage>() {
           @Override
-          public List<TableName> apply(ListTablesPagedResponse response) {
-            List<TableName> results = Lists.newArrayList();
-            for (com.google.bigtable.admin.v2.Table proto : response.iterateAll()) {
+          public ListTablesPage apply(ListTablesPagedResponse response) {
+            return response.getPage();
+          }
+        },
+        MoreExecutors.directExecutor()
+    );
+
+    // Fetch the rest of the pages by chaining the futures.
+    ApiFuture<List<com.google.bigtable.admin.v2.Table>> allProtos = ApiFutures
+        .transformAsync(
+            firstPageFuture,
+            new ApiAsyncFunction<ListTablesPage, List<com.google.bigtable.admin.v2.Table>>() {
+              List<com.google.bigtable.admin.v2.Table> responseAccumulator = Lists
+                  .newArrayList();
+
+              @Override
+              public ApiFuture<List<com.google.bigtable.admin.v2.Table>> apply(
+                  ListTablesPage page) {
+                // Add all entries from the page
+                responseAccumulator.addAll(Lists.newArrayList(page.getValues()));
+
+                // If this is the last page, just return the accumulated responses.
+                if (!page.hasNextPage()) {
+                  return ApiFutures.immediateFuture(responseAccumulator);
+                }
+
+                // Otherwise fetch the next page.
+                return ApiFutures.transformAsync(
+                    page.getNextPageAsync(),
+                    this,
+                    MoreExecutors.directExecutor()
+                );
+              }
+            },
+            MoreExecutors.directExecutor()
+        );
+
+    // Wrap all of the accumulated protos.
+    return ApiFutures.transform(allProtos,
+        new ApiFunction<List<com.google.bigtable.admin.v2.Table>, List<TableName>>() {
+          @Override
+          public List<TableName> apply(List<com.google.bigtable.admin.v2.Table> protos) {
+            List<TableName> results = Lists.newArrayListWithCapacity(protos.size());
+            for (com.google.bigtable.admin.v2.Table proto : protos) {
               results.add(TableName.parse(proto.getName()));
             }
             return results;
           }
         },
-        MoreExecutors.directExecutor());
+        MoreExecutors.directExecutor()
+    );
   }
 
   /**

google-cloud-clients/google-cloud-bigtable-admin/src/test/java/com/google/cloud/bigtable/admin/v2/BigtableTableAdminClientTest.java

@@ -33,6 +33,7 @@
 import com.google.bigtable.admin.v2.ListTablesRequest;
 import com.google.bigtable.admin.v2.ModifyColumnFamiliesRequest.Modification;
 import com.google.bigtable.admin.v2.TableName;
+import com.google.cloud.bigtable.admin.v2.BaseBigtableTableAdminClient.ListTablesPage;
 import com.google.cloud.bigtable.admin.v2.BaseBigtableTableAdminClient.ListTablesPagedResponse;
 import com.google.cloud.bigtable.admin.v2.models.ConsistencyToken;
 import com.google.cloud.bigtable.admin.v2.models.CreateTableRequest;
@@ -216,34 +217,52 @@ public void testGetTable() {
   @Test
   public void testListTables() {
     // Setup
-    ListTablesRequest expectedRequest = ListTablesRequest.newBuilder()
-        .setParent(INSTANCE_NAME.toString())
-        .build();
-
-    ListTablesPagedResponse expectedResponseWrapper = Mockito.mock(ListTablesPagedResponse.class);
+    com.google.bigtable.admin.v2.ListTablesRequest expectedRequest =
+        com.google.bigtable.admin.v2.ListTablesRequest.newBuilder()
+            .setParent(INSTANCE_NAME.toString())
+            .build();
 
-    Iterable<com.google.bigtable.admin.v2.Table> expectedResults = Lists.newArrayList(
-        com.google.bigtable.admin.v2.Table.newBuilder()
-            .setName(TABLE_NAME.toString() + "1")
-            .build(),
-        com.google.bigtable.admin.v2.Table.newBuilder()
-            .setName(TABLE_NAME.toString() + "2")
-            .build());
+    // 3 Tables spread across 2 pages
+    List<com.google.bigtable.admin.v2.Table> expectedProtos = Lists.newArrayList();
+    for (int i = 0; i < 3; i++) {
+      expectedProtos.add(
+          com.google.bigtable.admin.v2.Table.newBuilder()
+              .setName(TABLE_NAME.toString() + i)
+              .build());
+    }
+    // 2 on the first page
+    ListTablesPage page0 = Mockito.mock(ListTablesPage.class);
+    Mockito.when(page0.getValues()).thenReturn(expectedProtos.subList(0, 2));
+    Mockito.when(page0.getNextPageToken()).thenReturn("next-page");
+    Mockito.when(page0.hasNextPage()).thenReturn(true);
+
+    // 1 on the last page
+    ListTablesPage page1 = Mockito.mock(ListTablesPage.class);
+    Mockito.when(page1.getValues()).thenReturn(expectedProtos.subList(2, 3));
+
+    // Link page0 to page1
+    Mockito.when(page0.getNextPageAsync()).thenReturn(
+        ApiFutures.immediateFuture(page1)
+    );
 
-    Mockito.when(mockListTableCallable.futureCall(expectedRequest))
-        .thenReturn(ApiFutures.immediateFuture(expectedResponseWrapper));
+    // Link page to the response
+    ListTablesPagedResponse response0 = Mockito.mock(ListTablesPagedResponse.class);
+    Mockito.when(response0.getPage()).thenReturn(page0);
 
-    Mockito.when(expectedResponseWrapper.iterateAll())
-        .thenReturn(expectedResults);
+    Mockito.when(mockListTableCallable.futureCall(expectedRequest)).thenReturn(
+        ApiFutures.immediateFuture(response0)
+    );
 
     // Execute
     List<TableName> actualResults = adminClient.listTables();
 
     // Verify
-    assertThat(actualResults).containsExactly(
-        TableName.parse(TABLE_NAME.toString() + "1"),
-        TableName.parse(TABLE_NAME.toString() + "2")
-    );
+    List<TableName> expectedResults = Lists.newArrayList();
+    for (com.google.bigtable.admin.v2.Table expectedProto : expectedProtos) {
+      expectedResults.add(TableName.parse(expectedProto.getName()));
+    }
+
+    assertThat(actualResults).containsExactlyElementsIn(expectedResults);
   }
 
   @Test