Set the max number of driver instances to CPU cores

pool.go

@@ -3,9 +3,13 @@ package server
 import (
 	"fmt"
 	"math"
+	"runtime"
+	"strconv"
 	"sync/atomic"
 	"time"
 
+	"os"
+
 	"github.com/bblfsh/sdk/protocol"
 	"github.com/pkg/errors"
 )
@@ -235,7 +239,21 @@ type ScalingPolicy interface {
 // DefaultScalingPolicy returns a new instance of the default scaling policy.
 // Instances returned by this function should not be reused.
 func DefaultScalingPolicy() ScalingPolicy {
-	return MovingAverage(10, MinMax(1, 10, AIMD(1, 0.5)))
+	maxInstances := 0
+	// Try to read maxInstances from the environment variable
+	maxInstancesEnv := os.Getenv("BBLFSH_SCALING_MAX_INSTANCES")
+	if len(maxInstancesEnv) > 0 {
+		var err error
+		maxInstances, err = strconv.Atoi(maxInstancesEnv)
+		if err != nil {
+			maxInstances = 0
+		}
+	}
+	// Disregarding the fact that the env var exists or not and is valid or not
+	if maxInstances <= 0 {
+		maxInstances = runtime.NumCPU()
+	}
+	return MovingAverage(10, MinMax(1, maxInstances, AIMD(1, 0.5)))
 }
 
 type movingAverage struct {

pool_test.go

@@ -2,6 +2,7 @@ package server
 
 import (
 	"fmt"
+	"runtime"
 	"sync"
 	"testing"
 	"time"
@@ -121,7 +122,7 @@ func TestDriverPoolParallel(t *testing.T) {
 	}
 
 	wg.Wait()
-	require.Equal(10, dp.cur)
+	require.Equal(runtime.NumCPU(), dp.cur)
 
 	time.Sleep(time.Second * 2)
 	require.Equal(1, dp.cur)