Increase max thread count to 50k

Signed-off-by: Dong Chen <dongluo.chen@docker.com>

cli/cli.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"runtime/debug"
 
 	log "github.com/Sirupsen/logrus"
 	"github.com/codegangsta/cli"
@@ -13,6 +14,8 @@ import (
 
 // Run the Swarm CLI.
 func Run() {
+	setProgramLimits()
+
 	app := cli.NewApp()
 	app.Name = path.Base(os.Args[0])
 	app.Usage = "A Docker-native clustering system"
@@ -66,3 +69,11 @@ func Run() {
 		log.Fatal(err)
 	}
 }
+
+func setProgramLimits() {
+	// Swarm runnable threads could be large when the number of nodes is large
+	// or under request bursts. Most threads are occupied by network connections.
+	// Increase max thread count from 10k default to 50k to accommodate it.
+	const maxThreadCount int = 50 * 1000
+	debug.SetMaxThreads(maxThreadCount)
+}