Improve benchmark, fix offset bug

This ensures that setup time does not impact the results of the
benchmark since profiling showed that much time was spent setting up the
test array of tasks. This also uses `make` to build that slice instead.

Also, the tests revealed that there was a bug where offsets were
pre-incremented rather than post-incremented, omitting the first 100
results.

kapacitor/kapa_client.go

@@ -51,7 +51,6 @@ func (p *PaginatingKapaClient) ListTasks(opts *client.ListTasksOptions) ([]clien
 		}
 
 		for {
-			opts.Offset = p.FetchRate + opts.Offset
 			select {
 			case <-done:
 				close(optChan)
@@ -59,6 +58,7 @@ func (p *PaginatingKapaClient) ListTasks(opts *client.ListTasksOptions) ([]clien
 			case optChan <- *opts:
 				// nop
 			}
+			opts.Offset = p.FetchRate + opts.Offset
 		}
 	}()
 

kapacitor/kapa_client_benchmark_test.go

@@ -11,18 +11,20 @@ import (
 func BenchmarkKapaClient100(b *testing.B)    { benchmark_PaginatingKapaClient(100, b) }
 func BenchmarkKapaClient1000(b *testing.B)   { benchmark_PaginatingKapaClient(1000, b) }
 func BenchmarkKapaClient10000(b *testing.B)  { benchmark_PaginatingKapaClient(10000, b) }
+func BenchmarkKapaClient100000(b *testing.B) { benchmark_PaginatingKapaClient(100000, b) }
+
+var tasks []client.Task
 
 func benchmark_PaginatingKapaClient(taskCount int, b *testing.B) {
+
+	b.StopTimer() // eliminate setup time
+
 	// create a mock client that will return a huge response from ListTasks
 	mockClient := &mocks.KapaClient{
 		ListTasksF: func(opts *client.ListTasksOptions) ([]client.Task, error) {
 			// create all the tasks
-			allTasks := []client.Task{}
+			allTasks := make([]client.Task, taskCount)
 
-			// create N tasks from the benchmark runner
-			for i := 0; i < taskCount; i++ {
-				allTasks = append(allTasks, client.Task{})
-			}
 			begin := opts.Offset
 			end := opts.Offset + opts.Limit
 
@@ -42,8 +44,11 @@ func benchmark_PaginatingKapaClient(taskCount int, b *testing.B) {
 
 	opts := &client.ListTasksOptions{}
 
+	b.StartTimer() // eliminate setup time
+
 	// let the benchmark runner run ListTasks until it's satisfied
 	for n := 0; n < b.N; n++ {
-		_, _ = pkap.ListTasks(opts)
+		// assignment is to avoid having the call optimized away
+		tasks, _ = pkap.ListTasks(opts)
 	}
 }

kapacitor/kapa_client_test.go

@@ -26,6 +26,10 @@ func Test_Kapacitor_PaginatingKapaClient(t *testing.T) {
 				end = len(allTasks)
 			}
 
+			if begin > len(allTasks) {
+				begin = end
+			}
+
 			return allTasks[begin:end], nil
 		},
 	}