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"
 )
@@ -14,6 +18,11 @@ var (
 	// DefaultPoolTimeout is the time a request to the DriverPool can wait
 	// before getting a driver assigned.
 	DefaultPoolTimeout = time.Second * 5
+
+	// DefaultMaxInstancesPerDriver is the maximum number of instances of
+	// the same driver which can be launched following the default
+	// scaling policy (see DefaultScalingPolicy()).
+	DefaultMaxInstancesPerDriver = runtime.NumCPU()
 )
 
 // DriverPool controls a pool of drivers and balances requests among them,
@@ -235,7 +244,7 @@ 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)))
+	return MovingAverage(10, MinMax(1, DefaultMaxInstancesPerDriver, AIMD(1, 0.5)))
 }
 
 type movingAverage struct {
@@ -334,3 +343,14 @@ func (p *aimd) Scale(total, load int) int {
 
 	return res
 }
+
+func init() {
+	// Try to read DefaultMaxInstancesPerDriver from the environment variable
+	defaultMaxInstancesPerDriverEnv := os.Getenv("BBLFSH_MAX_INSTANCES_PER_DRIVER")
+	if len(defaultMaxInstancesPerDriverEnv) > 0 {
+		maxInstances, err := strconv.Atoi(maxInstancesEnv)
+		if err == nil && maxInstances > 0 {
+			DefaultMaxInstancesPerDriver = maxInstances
+		}
+	}
+}

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)