1 files changed, 51 insertions, 1 deletions

diff --git a/pkg/instance/instance.go b/pkg/instance/instance.go
index b393991d0..1a504fdd7 100644
--- a/pkg/instance/instance.go
+++ b/pkg/instance/instance.go
@@ -36,6 +36,7 @@ type Env interface {
 type env struct {
 	cfg           *mgrconfig.Config
 	optionalFlags bool
+	buildSem      *Semaphore
 }
 
 type BuildKernelConfig struct {
@@ -48,7 +49,7 @@ type BuildKernelConfig struct {
 	KernelConfig []byte
 }
 
-func NewEnv(cfg *mgrconfig.Config) (Env, error) {
+func NewEnv(cfg *mgrconfig.Config, buildSem *Semaphore) (Env, error) {
 	if !vm.AllowsOvercommit(cfg.Type) {
 		return nil, fmt.Errorf("test instances are not supported for %v VMs", cfg.Type)
 	}
@@ -67,11 +68,16 @@ func NewEnv(cfg *mgrconfig.Config) (Env, error) {
 	env := &env{
 		cfg:           cfg,
 		optionalFlags: true,
+		buildSem:      buildSem,
 	}
 	return env, nil
 }
 
 func (env *env) BuildSyzkaller(repoURL, commit string) (string, error) {
+	if env.buildSem != nil {
+		env.buildSem.Wait()
+		defer env.buildSem.Signal()
+	}
 	cfg := env.cfg
 	srcIndex := strings.LastIndex(cfg.Syzkaller, "/src/")
 	if srcIndex == -1 {
@@ -126,6 +132,10 @@ func (env *env) BuildSyzkaller(repoURL, commit string) (string, error) {
 
 func (env *env) BuildKernel(buildCfg *BuildKernelConfig) (
 	string, build.ImageDetails, error) {
+	if env.buildSem != nil {
+		env.buildSem.Wait()
+		defer env.buildSem.Signal()
+	}
 	imageDir := filepath.Join(env.cfg.Workdir, "image")
 	params := build.Params{
 		TargetOS:     env.cfg.TargetOS,
@@ -536,3 +546,43 @@ func RunnerCmd(prog, fwdAddr, os, arch string, poolIdx, vmIdx int, threaded, new
 	return fmt.Sprintf("%s -addr=%s -os=%s -arch=%s -pool=%d -vm=%d "+
 		"-threaded=%t -new-env=%t", prog, fwdAddr, os, arch, poolIdx, vmIdx, threaded, newEnv)
 }
+
+type Semaphore struct {
+	ch chan struct{}
+}
+
+func NewSemaphore(count int) *Semaphore {
+	s := &Semaphore{
+		ch: make(chan struct{}, count),
+	}
+	for i := 0; i < count; i++ {
+		s.Signal()
+	}
+	return s
+}
+
+func (s *Semaphore) Wait() {
+	<-s.ch
+}
+
+func (s *Semaphore) WaitAll() {
+	for i := 0; i < cap(s.ch); i++ {
+		s.Wait()
+	}
+}
+
+func (s *Semaphore) WaitC() <-chan struct{} {
+	return s.ch
+}
+
+func (s *Semaphore) Available() int {
+	return len(s.ch)
+}
+
+func (s *Semaphore) Signal() {
+	if av := s.Available(); av == cap(s.ch) {
+		// Not super reliable, but let it be here just in case.
+		panic(fmt.Sprintf("semaphore capacity (%d) is exceeded (%d)", cap(s.ch), av))
+	}
+	s.ch <- struct{}{}
+}